Four RS-25 engines, like the one pictured undergoing a hot-fire test, will power the core stage of NASA's Space Launch System (SLS) -- NASA's new heavy-lift launch vehicle. Formerly known as the space shuttle main engine, the RS-25 accumulated over 1 million seconds—or almost 280 hours — of hot fire experience during 135 missions and numerous related engine tests like the one pictured here.

For good measure here's a video of three 2-percent scale models of the RS-25 being test fired: